In my prior U.S. Pat. Nos. 4,228,770, issued Oct. 21, 1980, and 4,474,145 issued Oct. 2, 1984, there are disclosed various forms of fuel supply systems particularly adapted for use in internal combustion engines, especially two-cycle engines of the kind extensively employed in motorcycles and also in various industrial equipment, including power saws.
In many of such two-cycle engines, the fuel/air supply system includes a supply passage approaching the inlet opening in the cylinder wall, and further includes at least one ported wall positioned in a plane transverse to and usually obliquely inclined with respect to the axis of flow through the fuel/air supply passage. Quite commonly, a V-shaped reed cage is employed in such fuel supply systems, as is disclosed in my prior U.S. patents referred to above and also in the present application, the reed cage having a pair of inclined converging side walls joined in a reed cage apex presented downstream of the axis of flow through the supply passage. Reed valves are provided overlying the valve ports in the inclined ported walls. Although the reed cage may be positioned with its apex extended in various directions, it is preferred that the apex be generally horizontal as shown in various embodiments illustrated.
In fuel supply and valve arrangements of the kind referred to, in order to maintain maximum power output of the engine, especially at high operating speeds, it is of great importance to minimize fluctuations in the velocity of flow through the fuel/air supply system and through the valves and into the cylinder. Some appreciable reduction of fluctuations in the velocity of flow is provided in my prior U.S. patents above referred to by the provision of an interior element in the flow passage upstream of the valve ports, such element having an aerodynamic or airfoil contour so that velocity fluctuations in the fuel/air flow at and near the surfaces of the aeroform element are reduced, particularly at high engine speeds.
It is also of importance to minimize abrupt changes in the direction of flow of the fuel/air through the intake system and the valves and into the intake port of the engine, thereby minimizing fuel/air drag as the fuel/air flows through the intake system. Still further, it is of importance to avoid localized turbulence in various regions of the flow or supply passage.
The foregoing and other objectives of the present invention are accomplished by introducing a number of changes in the structure, contours and arrangements of the parts defining the flow passage at various regions along the flow path.
Some of the foregoing objectives are achieved by providing curvilinear surfaces surrounding the fuel/air flow passage or passages within the reed cage, such surrounding surfaces being of aerodynamic or airfoil contour within the reed cage and thereby minimizing flow velocity changes and providing for extensive reduction in turbulence at the perimeter of the flow passages within the reed cage as such passages merge with the portions of the port under the side edges and under the delivery end edge of the valve reed.
The passages through the reed cage are also arranged so as to avoid abrupt changes in the direction of flow within the reed cage.
As will further be seen, in certain embodiments of the present invention, provision is made not only for reducing the velocity fluctuations around the perimeter of the air/fuel flow stream, but this feature of the present invention may, in some embodiments, also be employed in combination with an aeroform element positioned within the passage in the reed cage similar to interior elements of the kind disclosed in my prior U.S. patents above identified, and this combination results not only in particularly effective reduction in velocity fluctuations but also in great reduction in turbulence.
Certain embodiments of the present invention further include a specially formed cavity in the engine housing for receiving the reed cage in the region of the inlet port through which the fuel/air is delivered from the reed cage. This cavity includes additional fuel/air passageways at the ends of the reed cage, formed in the engine housing structure beyond the end walls of the V-shaped reed cage. Such additional passages at each end of the reed cage generally parallel the adjacent inclined surface of the reed cage and are interconnected with a cavity or passageway formed in the engine housing structure beyond the reed cage apex and leading to the engine intake/porting. These additional external passages lie beyond each end of the reed cage and not only communicate with each other but also communicate with the fuel/air flow path downstream of the reed cage apex and thus also with the intake porting into the engine. All of these additional passages are preferably also of curvilinear contour in order to minimize abrupt changes in the flow path of the incoming fuel/air when the reed valves open the valve ports in the reed cage. In this way, portions of the fuel/air delivered from the valve ports at the end regions of the reed cage apex may spread laterally into passages of aeroform contour merging downstream of the apex and ultimately entering the intake porting in the engine housing structure.
The foregoing is particularly effective in minimizing the undesirable type of turbulence which frequently results from impingement of a fuel/air stream against a surface which is planar, rather than curvilinear.
In considering various aspects of the present invention, it should be kept in mind that in the operation of the engine at any speed, the flow of the fuel/air into the cylinder necessarily starts and stops with each cycle of the engine regardless of the speed of operation. However, the contours of the surfaces defining the flow passages extensively influence the character of the starts and stops of the flow. Flat surface areas perpendicular to the flow axis accentuate turbulence and unnecessarily increases kinetic energy loss when the flow starts and stops.
The flow passage arrangements provided according to the present invention are used in combination with certain valve porting and reed valve arrangements which also reduce turbulence and fluctuation of flow velocity in the flow path.
Unnecessary turbulence and secondary velocity fluctuations of the fuel/air flow tend to reduce the power output of the engine, in part, because of the waste of energy involved in unnecessary velocity changes. The fuel/air stream has kinetic energy, and increase or decrease of the flow velocity results in loss of kinetic energy, and at any speed of operation of the engine, unnecessary fluctuations of velocity results in substantial energy loss. Avoiding rapid fluctuations of the flow velocity also diminishes turbulence in areas where the flow path is required to shift in direction, and this further reduces waste of energy in engine operation.